Sexual contact is often important in the formation and maintenance of social attachments. These studies will examine the role of sensory stimuli associated with mating, specifically those arising from pelvic viscera, in the formation of social attachments. Using voles as a model system, we will first perform a comparative analysis of the patterns of mating-induced neuronal activation in closely related vole species that differ in their social systems. We will concentrate on forebrain and brainstem areas associated with the mediation of social attachment and with the processing of sensory input from the pelvic viscera. We will then combine behavioral and immunocytochemical measures to examine the effect of interruption of mating-specific sensory input on pair-bond formation. The results of these studies will provide information on the link between social/sexual interactions and the formation of social attachments. Since deficits in the ability to form lasting social attachments are often associated with neuropsychiatric disorders in humans, understanding the neurobiology of social attachment may provide insights into the underlying causes of such disorders.